The present invention relates to a downhole pumping system used to pump fluid from a well, such as a petroleum recovery well, to the surface through a production tubing string within the tubing string. More particularly, this invention relates to equipment and techniques which allow the installation and retrieval of the downhole pump without requiring the removal of the production tubing string from a well, thereby saving significant costs.
Downhole pumps have been used for decades to pump fluids from a petroleum well to the surface. Pumps are generally classified as reciprocating pumps, wherein the drive member to the pump is a reciprocating rod within the tubing string, or progressive cavity pumps, wherein the pump is powered by a rotating rod string within the tubing string. A third type of downhole pump is an electrically powered submersible pump, and a fourth type is a jet pump. The electrically powered pump and the jet pump do not transmit a pumping force downhole on a rod string to power the pump.
It is periodically necessary to retrieve the downhole pump to a surface for inspection and/or repair. In many situations, this requires the retrieval of the pump with the production tubing string, which may be thousands of feet in length. The operation of running the tubing string and downhole pump from the well and thereafter running the tubing string and the repaired pump back in the well may cost thousands of dollars. Moreover, hydrocarbon production may be adversely affected by the tubular breakout and subsequent run in operation, including damage to the pipe or other casing surrounding the tubing string, and/or damage to the tubing string or the repaired pump. In some operations, the process of repairing the pump involves both the time and expense associated with recovering the tubing string, and thereafter patching or repairing the casing string before the repaired pump and tubing string are run back into the well.
Various mechanisms have been suggested for allowing the retrieval of a downhole pump without requiring the retrieval of the tubing string. U.S. Pat. No. 5,005,651 discloses a hold-down mechanism for selectively holding a pump in place on the tubing string, but also for releasing the pump so the pump can be retrieved while the tubing string remains in the well. More particularly, the tubing string is lowered to unseat the hold-down from a seating nipple, so that an upward force is applied on an adapter. U.S. Pat. No. 5,636,689 disclose a technique for retrieving a downhole tool while preventing premature actuation of the tool during insertion into a well. During retrieval, a pin is released from a slot, allowing the collapse of a C-ring to a reduced diameter, so that a lower cone pulls away from a mandrel. U.S. Pat. No. 5,746,582 also discloses a pump for lifting formation fluids to the surface while allowing the pump to be retrieved through the production tubing. The pump is retrievably positioned within the production tubing string and is releasably connected to a downhole motor which is driven by electrical power. To release the pump, the polarity of current to the motor is reversed. U.S. Pat. No. 6,089,832 discloses another downhole pump intended to be retrieved and reinstalled through the production tubing string while leaving the tubing string in place in the well. To retrieve the pump, one member moves upward to engage a seat, which equalizes pressure to reduce the upward force required to unlatch the pump.
Many of the techniques for allowing retrieval of a pump while leaving the tubing in place are complex and thus costly, and also require components which have a relatively short life. Improved techniques are required for obtaining the advantages of a downhole pump which can be retrieved to the surface through the production tubing string. The disadvantages of the prior art are overcome by the present invention, and an improved downhole pump system and technique for installing and retrieving the downhole pump are hereinafter disclosed.
The downhole pump system according to the present invention comprises a pump housing, a mandrel movable relative to the pump housing to pump fluid, a drive rod, a drive coupling and a lifting nut. The drive rod may be connected to the pump for either rotating or reciprocating the mandrel relative to the pump housing, thereby pumping fluid to the surface. The pump may be inserted into a production tubing and pushed along the production tubing by the drive rod.
Axial movement of the pump with the drive rod for a progressive cavity pump may be provided by the drive rod being attached to the rotor by a drive coupling. Thrust may be applied when pushing by the end of the rotor contacting the mandrel. When lowering or pulling the pump, tension may be applied by the drive coupling contacting the lifting nut.
The pump may be secured in the casing by engaging the in the pump housing with a landing nipple positioned along a lower end of the production tubing string, with the landing nipple including a locking groove. Axial movement of the pump housing may be restricted by a spring lock mechanism, which preferably is a radially expandable and collapsible C-ring. Rotation of the pump housing may be prevented by the use of a spine, key, or similar rotation limiting surfaces on the pump housing and the landing nipple. Fluid leakage and/or solids migration may be prevented by the combination of fluid and debris seals.
It is a feature of the present invention that radial seals are provided at the upper end of the housing, and may include brush, elastomeric, energized, deformable, non-contact, packing, and grease type seals. A related feature of the invention is that compression seals are provided at the lower end of the housing. Again, these seals may include brush, elastomeric, energized, deformable, non-contract, packing, and grease type seals. A reduced radius annular seal is also preferably provided at the lower end of the housing, and may be any of the type of seals discussed above. Each of the seals preferably has a diameter less than an inner nominal diameter of the production tubing string, thereby minimizing wear on the seals and the tubing when running the pump into and out of the interior of the production tubing string.
The pump may include a reduced diameter leading edge for inserting the pump into the pipe or other casing, and for engagement of the pump housing into the landing nipple. A spring and groove system, preferably having a C-ring carried on the landing nipple for engagement with an external groove in the pump housing, may be used to restrict axial movement of the pump housing. The spring may be a ring, leaf, Belleville, coil or torsion type spring, and may be provided with or without a latching mechanism mounted with the spring, so that a latch rather than the spring engages the external groove in the pump housing. The spring may be fixed or floating, and cooperates with the groove to limit axial movement of the pump housing.